The first thing you should do to fix the problem is launch the Firefox installer as an administrator. It might be a lack of necessary administrator permissions that is causing hurdles in installing Firefox on your PC. So, you can simply run the installer with administrator rights and see if the problem is resolved.

To do so, open File Explorer using Win+E and go to the Downloads or the folder where you have downloaded the setup file of Firefox. Now, right-click on the setup file and click on the Run as administrator option from the appeared context menu. Next, follow the prompted instructions and see if you are able to successfully install Firefox or not.

2] download a fresh setup file

It might be the case that you are facing the issue because of an incomplete or corrupted installer file. The download process might be interrupted due to network issues. Also, if you are using an old installer file to install Firefox, it might not install. Hence, if the scenario is applicable, you can delete the existing setup file and then download the latest installer file from the official website of Firefox or the Microsoft Store. See if you are now able to install the Firefox browser or not.

If you downloaded the setup from Microsoft Store, try downloading Firefox from its website instead of the Microsoft Store and see.

As reported by some users, they can’t download and install Firefox from Microsoft Store. If the same is applicable to you, download the Firefox installer from its official website and then try installing it on your computer.

On the other hand, if you are unable to install Firefox using its setup file, you can try installing the browser from Microsoft Store.

3] Completely uninstall Firefox from your PC and then reinstall it

In case you are trying to reinstall Firefox on your computer, you must uninstall it completely from your computer to avoid any issues. Apart from that, if you are facing this issue while trying to update your browser, you can first uninstall Firefox and then install its latest version to fix the issue.

To completely uninstall Firefox from Windows, follow the below steps:

First, press Win+I to open the Settings app and navigate to the Apps tab. Then, click on the Installed apps option and select the Mozilla Firefox app from the list of installed apps.

After that, press the three-dot menu button present next to Firefox and choose the Uninstall option. You now have to follow the instructions prompted on your screen and complete the app removal process.

When done, open File Explorer using Win+E and navigate to the C:\Program Files folder. From here, delete the Mozilla Firefox folder. Next, delete the Firefox folder from the C:\Program Files (x86) location as well.

Next, open the Run dialog using Win+R and enter the following address in its Open field:

%APPDATA%\Mozilla\

In the opened location, delete all the files and folders.

Now, restart your computer and download the latest installer for Firefox from its website. Hopefully, you will now be able to install Firefox without any issues.

Read: Firefox Spell Checker not working on Windows.

4] Manually update Firefox

In case the issues occur when you are trying to update Firefox using its installer, you can manually update Firefox. Open Firefox, click on the three-bar menu button and choose the About Firefox option. Now, let Firefox look for available software updates. Once done, you can install the updates and restart the browser to complete the process.

5] Temporarily disable your antivirus/firewall

It could be your overprotective security program causing issues while installing Firefox. It might be preventing you from installing Firefox on your computer. Hence, it is suggested to temporarily disable your antivirus/firewall and then try installing Firefox on your PC. After the browser is installed, you can enable your security programs again.

Hope this helps.

If the problem still remains the same and you are unable to install Firefox on your computer, no worries. There are several good free web browsers available that you can use as an alternative and perform your tasks. Some of the nice ones you can use are Google Chrome, Microsoft Edge, Pale Moon, Opera, OperaGX, and many more. If you want a secure and private browser, you can try Epic Privacy Browser, Tor, Iridium Browser, etc.

Why doesn t Firefox work on Windows 11?

If the Firefox browser installed on your computer but not working properly, some problematic add-ons might be causing this issue. A corrupted Firefox startupCache can be another reason for the same. Besides that, if the browser is corrupted or there are certain installation files that are broken, Firefox won’t work properly.

Now read: Firefox keeps crashing on Windows PC.

As the app in question is a Microsoft Store app, you can begin troubleshooting to resolve the This app can’t be activated by the Built-in Administrator issue that has occurred on your Windows 11/10 device by running the Windows Store Apps Troubleshooter and see if that helps.

To run Windows Store Apps Troubleshooter on your Windows 11 device, do the following:

• Press Windows key + I to open Settings app.
• Navigate to System > Troubleshoot > Other troubleshooters.
• Under the Other section, find Windows Store Apps.
• Click Run button.
• Follow on-screen instructions and apply any recommended fixes.

To run the Windows Store Apps Troubleshooter on your Windows 10 PC, do the following:

• Press Windows key + I to open Settings app.
• Go to Update and Security.
• Click the Troubleshooter tab.
• Scroll down and click on Windows Store Apps.
• Click the Run the troubleshooter button.
• Follow on-screen instructions and apply any recommended fixes.

If this didn’t help, you can uninstall and reinstall the Windows Store app in question.

2] Run System File Checker (SFC) scan

This solution requires you to run SFC scan on your Windows 11/10 PC and see if that helps. The native utility will repair any corrupt system file which is a likely culprit to the issue in hand.

3] Reset Microsoft Store or Clear Windows Store Cache

Some affected users reported they were able to resolve the issue in hand by resetting Microsoft Store or clearing Windows Store cache. So, you can give this a try and see if that works for you, otherwise try the next solution.

4] Change UAC level

Due to security setting of newer versions of Windows, certain file types that are opened through Store apps will require UAC (User Account Control) permissions in order to run, but since the built-in account doesn’t have UAC privileges, you’ll get the error. In this case, to resolve the issue, you can change the UAC level on your Windows 11/10 PC.

Try the next solution if this didn’t work for you.

5] Modify User Account Control policy via Group Policy Editor

This is a two-step solution which requires you to enable Admin Approval Mode for the Built-in Administrator Account and then modify the User Interface Privilege Isolation (UIPI) registry key value.

Do the following:

• Press Windows key + R to invoke the Run dialog.
• In the Run dialog box type gpedit.msc and hit Enter to open Group Policy Editor.
• Inside the Local Group Policy Editor, use the left pane to navigate to the path below:

Computer Configuration > Windows Settings > Security Settings > Local Policy > Security Options

• Scroll on the right pane, locate and double-click on User Account Control: Admin Approval Mode for the Built-in Administrator account policy to edit its properties.
• In the policy window, set the radio button to Enabled.
• Click Apply > OK to save the changes.
• Exit Group Policy Editor.

For Windows 11/10 Home users, you can add Local Group Policy Editor feature and then carry out the instructions as provided above.

Now, you can proceed with the step 2 to modify the UIPI registry key value.

Since this is a registry operation, it is recommended that you back up the registry or create a system restore point as necessary precautionary measures. Once done, you can proceed as follows:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\UIPI

• At the location on the right pane, double-click on the (Default) entry to edit its properties.
• In the properties dialog, input 0x00000001(1) in the Value data field.
• Click OK or hit Enter to save the change.
• Exit Registry Editor.
• Restart PC.

Hope this helps!

Related post: Microsoft Edge can’t be opened using the built-in administrator account

How do I enable the built-in administrator account?

To enable the built-in Administrator Account in Windows 11/10 PC, follow these instructions:

• Open Command Prompt in elevated mode.
• Type net user administrator /active:yes, and then hit Enter.
• Wait for confirmation.
• Restart your computer, and you will have the option to log in using the administrator account.

What is built-in administrator account?

The built-in administrator account in the Windows operating system (OS) is the first account created when the operating system is installed. You can also delete the built-in Administrator Account in Windows.